The invention relates to a method for heating an apparatus driven by a brushless DC motor, wherein stator coils of the brushless DC motor have an electric voltage applied to them during a heating phase.
The invention further relates to a control device for carrying out the method.
In motor vehicles propelled by a diesel internal-combustion engine a catalytic converter arranged in the exhaust passage can be employed for selective catalytic reduction (SCR) for the purpose of lessening the emission of nitrogen oxides in the exhaust gas. In this connection, a 32.5 percent solution of urea and water (Ad-Blue) from a storage reservoir is added in metered amounts to the exhaust gas upstream of the catalytic converter via a pump system and a nozzle with a pressure from 4.5 bar to 8.5 bar. The solution of urea and water freezes below −11° C. Therefore the storage-and-metering system has to be heated at low temperatures.
The solution of urea and water which is located in the storage reservoir is heated with a heating unit in the interior space of the storage reservoir. This heater heats up the solution of urea and water around the heater, an ultrasonic sensor for determining the filling level, the filter system and the intake-point. But the heating power is not sufficient to thaw out the complete hydraulic system of the metering system. The hydraulic pump system—also called the conveyor module—has to be heated additionally. For reasons of cost, a specific heating unit in the region of the hydraulic duct system is not provided. In order to thaw out the conveyor module, the pump is energized, in order, via the waste heat of the coil and the thermal linkage thereof to the mechanism and to the hydraulic ducts, to thaw out the latter and to keep them thawed out. The heating of the coil of the pump penetrates as far as the solution of urea and water via an armature and via a pump diaphragm. In some cases, thermal conductors are also provided in the conveyor module in such a way that the heat is directly conducted to the ducts.
A program flow provided in a control unit for the conveyor module determines, at the same time, the temperature of the solution of urea and water via a temperature sensor incorporated within the ultrasonic sensor for determining the filling level, the starting temperature of the coil (the temperature at the first moment without starting the heating function), and also takes the external temperature of the vehicle into consideration in the calculations. The coil temperature is monitored and also regulated over the entire heating process. Consequently it is ensured that the coil has the optimal heating temperature—that is to say, it does not introduce too little heat into the hydraulic system—but also that the coil does not become too hot, because otherwise a burn-out of the coil wire or damage to the pump mechanism may occur.
Coils in pump systems with reciprocating pumps have an internal resistance of, typically, 4 ohms. In the case of a regulated current in the “heating” operating mode of 2 amps, a power of 16 watts consequently results. If the mechanical drive of the pump is to be undertaken with a brushless DC motor (BLDC motor), this has a disadvantageous effect on the operation of the heating system. A brushless DC motor exhibits on its stator three stator coils arranged in a delta circuit or in a star circuit, and each stator coil may, in turn, have been split up into two or more partial stator coils. In operation, the three stator coils have voltage pulses, each offset by 120°, applied to them, and in this way generate a rotating field which drives a rotor equipped with permanent magnets. Each of the three stator coils, typically with 0.5 ohms, is of distinctly lower resistance than the coil of a reciprocating pump. The low resistance of the stator coils is necessary in order that a triggering of the brushless DC motor with a pulse-width-modulated triggering voltage is possible. In the following, the wiring of the brushless DC motor in a delta circuit will be considered. If the stator coils of the brushless DC motor are connected to a power supply via two of the three terminals for the purpose of heating, a parallel circuit arises consisting of a stator coil with a series connection of two stator coils. This arrangement has a resistance of 0.33 ohms and delivers a heating power of only 1.32 watts in the case of a flow of current of 2 amperes. An increase in the current through the stator coils, in order that a heating power comparable to a reciprocating pump is delivered, is not possible, since the stator coils are not designed for such a high current, and the strong magnetic field generated by them might then also demagnetize the permanent magnets of the rotor.
From DE 10 2013 216 785 A1 a washing machine is known with a control device for controlling a program flow, with a drum supported in a lye-container so as to be capable of rotating about a drum shaft, with an electric drive motor arranged outside the lye-container behind a lye-container wall, comprising a stator and a rotor, said drum shaft being driven directly by the rotor. In accordance with the invention there is provision that a heat-conducting connecting element, which consists of one or more heat-conducting components, is arranged between the interior space of the lye-container and the electric drive motor in such a way that the heat-conducting connecting element is in direct contact with the interior space and is able to transfer waste heat arising from an operation of the drive motor for the direct heating of an aqueous liquid located in the interior space of the lye-container.
Document DE 10 2013 109 522 B4 discloses a pump with a canned motor which exhibits a stator (1) with an internal rotor (17) arranged therein, wherein the stator (1) and the internal rotor (17) are separated from one another in liquid-tight manner by a split tube (21), arranged between the stator (1) and the internal rotor (17), which is made of a non-metallic material, wherein the stator (1) exhibits stator teeth (5) which extend radially in the direction of the internal rotor (17) and define with associated stator-tooth end faces (13) a receiving space for the internal rotor (17) and the split tube (21), wherein the split tube (21) bears against the stator-tooth end faces (13) and exhibits on its surface (23) facing toward the stator (1), in stator-tooth gaps (25) which are each defined by two mutually adjacent stator teeth (5), positively fitted ribs (27; 27a; 27b) which, starting from a rib foot (29) arranged on the split tube (21), taper in the radial direction with regard to a height (H), defined in the circumferential direction (U) of the split tube (21), of the ribs (27; 27a; 27b), wherein a stator tooth (5) consists of, respectively, a stator-tooth shank (7) and a stator-tooth head (11) which exhibits two stator-tooth-head parts (51a, 53a; 51b, 53b) which respectively rise above the stator-tooth shank (11) in both circumferential directions of the split tube (21), characterized in that rib flanks formed by side lines (39a, 40a; 39b, 40b) of the ribs (27; 27a; 27b) over the region of the height (H) of the ribs (27; 27a; 27b) are respectively in contact with a contour of the stator-tooth-head parts (51a, 53a; 51b, 53b) which is shaped so as to be complementary to the side lines (39a, 40a; 39b, 40b) as points of support fixed so as to counter shearing, wherein the stator-tooth contour and hence the height (H) of the ribs (27; 27a; 27b) is designed in such a way that under operating-pressure loading in the entire region of the split tube (21) equivalent stresses in the split tube (21) are always less than the strength limit of the split-tube material.
Document DE 10 2012 206 822 A1 describes a control unit (1) for triggering a brushless DC motor (3), said control unit (1) being designed to supply the DC motor (3) with energy. In accordance with the invention there is provision that the control unit (1) has further been designed to heat up the DC motor (3), by the DC motor (3) being supplied with energy without an alternating electromagnetic field thereby arising in the DC motor (3).
Publications DE 10 2013 216 785 A1 and DE 10 2013 109 522 B4 deal with utilization of the waste heat arising in operation of a brushless DC motor for the purpose of heating up liquids. A separate heating operation without a rotary motion is not provided.
Document DE 10 2012 206 822 A1 describes a control unit and an operating method that make it possible to employ a brushless DC motor, on the one hand, as drive unit with a rotary motion and, secondly, for the purpose of heating without rotary motion. In contrast to the present invention disclosure, however, there is no provision to alter the circuit arrangement of the coil windings of the brushless DC motor for the purpose of improving the heating power.